1. Field of the Invention
The invention presents a method and system for performing hyperspectral detection.
2. Description of the Related Art
Timely detection of targets continues to be a top priority for hyerspectral remote sensing capability. A hyperspectral sensor measures the radiance emanating from each pixel in a scene at multiple wavelengths, creating a datacube of the scene. The hyperspectral community has been trying over the past several years to operationalize this technology. One of the difficulties has been characterizing the intervening atmosphere between the target and the sensor.
Traditionally, atmospheric compensation techniques are applied, either empirically or through modeling, to transform the at-sensor radiance datacube to a surface reflectance datacube. Once in reflectance space, the spectra of each pixel can be compared to spectral reflectance libraries. This conversion has worked well for applications such as land use identification and mineralogy classification. This approach, though, is not optimal for time-critical detection of targets. First, it is computationally expensive to perform such a pixel-by-pixel transformation. Second, the resulting reflectance cube contains artifacts near absorption bands that are difficult to account for in near real-time. Finally, this approach does not lend itself well to scenes with significant illumination variability, such as the detection of shadowed targets.
One proposed atmospheric compensation technique is called the ‘invariant subspace method’ (Healey and Slater, IEEE Trans. Geosci. Remote Sensing, vol. 37, pp. 2706–27 17, Nov. 1999), incorporated herein by reference. In this approach, target reflectance spectra are projected to the at-sensor radiance domain using MODTRAN (a radiative transfer code). This method uses climatological parameters to produce literally thousands of signatures to simulate all possible atmospheric and illumination conditions and is a computational burden on the mission planner and on the target detection processor and thus not optimal for the tactical environment.